Limit switch assembly including rotatable cam with longitudinally guided indexing nut and cam longitudinal displacement means

ABSTRACT

A switch assembly provides position signals from a series of switches as a function of motor shaft rotation. A lead screw, rotated as a function of motor shaft rotation, includes an exterior threaded surface and a plurality of longitudinal slots. An indexing nut rides on the lead screw, but the indexing nut is restrained against rotation. A rotatable cam body has a plurality of drive tangs which extend into the lead screw slots, to afford rotation of the cam body in accordance with lead screw rotation. A bearing with a pair of snap rings translates the longitudinal movement of the indexing nut into a corresponding longitudinal displacement of the cam body. The cam has a lobe positioned to contact and selectively actuate the extending portions of a series of switches as the cam body is rotated and displaced lengthwise.

United States Patent 1 [1 11 9 Kelly et al. l 5lMarch 20, 1973 54] LIMIT SWITCH ASSEMBLY 3,462,563 8/1969 Henderson ..200 47 x X LONGITUDINALLY GUIDED Primary Examiner-J. R. Scott INDEXING NUT AND CAM LONGITUDINAL DISPLACEMENT MEANS Inventors: Robert R. Kelly, Hoffman Estates;

Donald H. Ward, Glen Ellyn, both of I11.

Assignee: Borg-Warner Corporation, Chicago,

Filed: May 4, 1971 Appl.No.: 140,192

References Cited UNITED STATES PATENTS 9/ 1960 Miller ..200/47 Attorney-Donald W. Banner and William S. McCurry [5 7] ABSTRACT A switch assembly provides position signals from a series of switches as a function of motor shaft rotation. A lead screw, rotated as a function of motor shaft rotation, includes an exterior threaded surface and a plurality of longitudinal slots. An indexing nut rides on the lead screw, but the indexing nut is restrained against rotation. A rotatable cam body has a plurality of drive tangs which extend into the lead screw slots, to afford rotation of the cam body in accordance with lead screw rotation. A bearing with a pair of snap rings translates the longitudinal movement of the indexing nut into a corresponding longitudinal displacement of the cam body. The cam has a lobe positioned to contact and selectively actuate the extending portions of a series of switches as the cam body is rotated and displaced lengthwise.

5 Claims, 2 Drawing Figures Fl" A PATENTEDHARZOIQYS 3721.780

Power Input F|G.1 M 24 22 V I5 Relay giagmfi 23 I I I I H 5 -%fi i A s s gri bl lr wentors 4 Roberf R. Kelly FIG 2 Donald H. Word LIMIT SWITCH ASSEMBLY INCLUDING ROTATABLE CAM WITH LONGITUDINALLY GUIDED INDEXING NUT AND CAM LONGITUDINAL DISPLACEMENT MEANS BACKGROUND OF THE INVENTION Many machines have a mechanism for driving a carriage or work piece as a function of an input command, and halting carriage movement when the equipment reaches the preassigned location. For example with a machine tool or a lathe it is desired to displace a carriage as a function of drive motor operation, and then to halt carriage movement at an exact location. Over a carriage travel length of 180 inches, the best positioning accuracy generally obtainable with most commercial equipment is of the order of 4 percent. This accuracy is not sufficient for drive systems which require very precise positioning.

It is therefore a primary consideration of the present invention to provide a switch assembly particularly useful in connection with such a drive system, for provid' ing control signals to indicate longitudinal travel with a much higher degree of precision than has heretofore been possible.

SUMMARY OF THE INVENTION The switch assembly of this invention is useful for providing control signals as a function of angular motion to indicate length of longitudinal displacement derived from the angular motion, for example, when a motor drives a carriage or other unit. The switch assembly includes a lead screw, which has a first portion positioned to receive rotational drive similar to the angular rotation of the motor shaft. The lead screw includes a second portion, which is threaded on its exterior, and the threads are interrupted to define at least one longitudinal slot. An indexing nut is provided, and has a threaded bore portion dimensioned to receive the exterior threads of the lead screw. Means is provided to prevent rotation of the indexing nut as it is displaced longitudinally by rotation of the lead screw. In a preferred embodiment this means included a pin extending from the indexing nut into a guide slot provided in the switch body. A cam body is provided with at least one interior tang portion extending into the longitudinal slot of the lead screw. The cam body also includes an exterior lobe. Means is also provided to effect longitudinal displacement of the cam body as a function of the longitudinal displacement of the indexing nut. In one embodiment this means included a bearing and a pair of end pins, one pin in the indexing nut and one in the cam body, so that the longitudinal motion is transferred while the cam body is rotated. A plurality of switches are provided, with their actuating portions extending adjacent the path of travel of the lobe on the cam body. In this way selective actuation of the switches is provided by the cam lobe as it is moved along its path of travel. Control signals are provided to regulate associated equipment as the lead screw is rotated in accordance with angular motion of a motor shaft or any other rotational signal.

THE DRAWING In the drawing figures, like reference numerals identify like elements, and in the drawing:

FIG. 1 is a block diagram indicating the employment of this invention in a larger system; and

FIG. 2 is a side view, partly in section and partly broken away, illustrating details of the switch assembly of this invention.

GENERAL SYSTEM DESCRIPTION FIG. 1 depicts a motor control arrangement in which the switch assembly of this invention is useful. As

there shown, a motor 11 is energized over line 12, relay 13, and power input line 14. When energized motor 11 provides mechanical power to a load (not shown) over a shaft 15, and the angular motion of shaft 15 is translated over shaft extension 16, flexible coupling 17, and shaft 18 to switch assembly 10. Of course shafts l5 and 16 can be the same component, or a pulley, sprocket arrangement, or other system can be utilized to drive input shaft 18 of the switch assembly as a function of the rotation of motor shaft 15.

Switch assembly 10 has a plurality of output conductors 20, shown gathered into a single cable 21, to transfer position-indicating control signals to a control circuit 22, which also includes a knob 23 or other arrangement for pre-setting a desired location signal. Responsive to coincidence between the preset location signal received over knob 23 and the instantaneous position signal on cable 21, control circuit 22 provides an output signal over conductor 24 to activate relay 13 and interrupt energization of motor 11. Other system configurations will be suggested to those skilled in this art. The present invention resides principally in the construction of switch assembly 10, to receive a mechanical input signal denoting angular movement over shaft 18, and provide output control signals over conductors 20 to afford a precise indication of the input shaft displacement.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 2, switch assembly 10 includes a cup-shaped housing 25 and a cover plate 26, affixed to housing 25 by a pair of fastening screws 27. Only one fastening screw is visible in FIG. 2. A lead screw 28 has a first portion 18 extending through a bore of cover plate 26 to receive rotational drive which is a function of the angular displacement of motor shaft 15. Lead screw 28 also includes a threaded portion 30, and at least one cam drive slot 31 which extends along the body of the lead screw and interrupts the threads. In a preferred embodiment four slots 31 were provided at intervals around the lead screw. The right end portion of lead screw assembly 28 includes a reduceddiameter end 50, received in a bearing 51 which in turn is snuggly fitted into a bore in the end of housing 25. A washer 52 and a nut 53 are provided to secure the right end of the lead screw assembly in position. The other end of the lead screw assembly, where it enters cover plate 26, is received in another bearing 54.

An indexing nut 32 has its bore portion tapped for mating engagement with lead screw threads 30, so that ordinarily the indexing nut would turn freely on the lead screw. However an indexing pin 33 has one end anchored in indexing nut 32 as shown, and the other end of pin 33 is received in a guide slot 34 defined in the interior surface of housing 25. Accordingly pin 33 and slot 34 cooperate to prevent rotation of the indexing nut; with rotation of lead screw assembly 28, indexing nut 32 is displaced longitudinally.

A cam body 35 is provided with at least one exterior lobe 36. The cam body is generally C-shaped (in section) as shown, and includes at least one tang or spline 37, sized to fit in longitudinal slot 31 of the lead screw assembly 28. In a preferred embodiment four tangs were provided, one tang being indexed in each of the four slots 31. Accordingly cam body 35 is rotated by angular movement ofthe lead screw assembly.

A bearing 38 is disposed between cam body 35 and indexing nut 32. The interior surface of bearing 38 is received against a shoulder portion of nut 32 and held in place by a snap ring 40. The outer portion of bearing 38 is similarly received in a cut-down portion of cam body 35 and held by a snap ring 41. With this arrangement bearing 38 cooperates with snap rings 40, 41 to provide a longitudinal displacement of cam body 35 as a function of longitudinal displacement of indexing nut 32.

From the foregoing description it is evident that as first portion 18 of lead screw 28 is rotated, cam body 35 is both rotated and moved longitudinally. Thus cam lobe 36 describes a spiral path of travel to sequentially engage the actuator portions 42 of each switch unit 43 as the lobe passes adjacent that switch unit. The control signal signifying shaft position is provided by displacement of the actuator. If desired this mechanical signal can be utilized for example, as a control signal for a fluid valve. In the illustrated embodiment switch 43 is of the type which provides an electrical signal at a pair of contacts 44, 45 to which the conductors shown generally as lines 20 in FIG. 1 can be attached. A pair of mounting plates 46 is provided; only one plate is visible in FIG. 2. Each switch mounting plate 46 is affixed by screws (not shown) within housing 25. A mounting screw 47 and spring 48 are provided so that the position of each switch can be simply and swiftly adjusted. Thus with rotation of lead screw 28 and actuators 42 of the screws 43 are sequentially displaced to provide an accurate indication of the rotation of the motor shaft.

SUMMARY By providing the combination of lead screw, nonrotating indexing nut, and a cam body which moves both longitudinally and rotationally, the switch assembly signals the carriage location with a high degree of accuracy. When single-turn rotary switches with conventional gearing have been employed in earlier arrangements, accuracy of the order of 4% was achieved to signal the carriage position. With the switch arrangement of this invention accuracies of the order of 0.1 percent can be achieved. The switch assembly of this invention has few parts, and is readily assembled and installed.

The indexing cam can provide a signal for both directions of rotation. The cam must have equal approach and fall-off slope angles with approximately 3.6 of switch actuation cam rotation angle to provide an accuracy of 0.1 percent in 3,600 degrees of total input shaft rotation.

While only a preferred embodiment of the invention has been described and illustrated, it is manifest that various modifications and alterations be made therein. It is therefore the intention in the appended claims to cover all such modifications and alterations as may fall within the true spirit and scope of the invention.

What is claimed is:

l. A switch assembly for providing control signals as a function of angular motion, comprising:

a lead screw, having a first portion positioned to receive rotational drive, and a second portion which is both threaded and defines at least one longitudinal slot;

an indexing nut, having a threaded bore portion dimensioned to receive the exterior threads of the lead screw;

means for preventing rotation of the indexing nut as it is displaced longitudinally by rotation of the lead screw;

a cam body, spaced from the indexing nut, including at least one interior tang portion extending into the longitudinal slot of the lead screw, and having at least one exterior lobe;

means, engaging both the cam body and the indexing nut, for effecting longitudinal displacement of the cam body as a function of the longitudinal displacement of the indexing nut, concomitantly with the angular displacement of the cam body as the lead screw is rotated; and

a plurality of switches disposed adjacent the path of travel of the lobe on the cam body, for selective actuation by the lobe to provide the control signals as the lead screw is rotated.

2. A switch assembly as claimed in claim 1, in which said lead screw defines a plurality of additional longitudinal slots, and said cam body includes a plurality of additional interior tang portions extending into the respective additional longitudinal slots of the lead screw.

3. A switch assembly as claimed in claim 1, in which the means for preventing rotation of the indexing nut includes a guide slot in the switch assembly, and an indexing pin, having one end received in the indexing nut and the other end extending into the guide slot, thus to prevent rotation of the indexing nut as it is driven by rotation of the lead screw.

4. A switch assembly as claimed in claim 1, in which the means for effecting longitudinal displacement of the cam bodyincludes a bearing, positioned between the cam body and the indexing nut, and a pair of snap rings, to assist in translating the longitudinal motion of the indexing nut to the cam body.

5. A switch assembly for providing control signals to de-energize a motor responsive to a preassigned rotational displacement of the motor shaft, comprising:

a housing for the switch assembly;

a lead screw, having a first portion positioned to receive rotational drive as a function of motor shaft rotation, and a second portion which is both threaded and defines a plurality of longitudinal slots;

an indexing nut, having a threaded bore portion dimensioned to receive the exterior threads of the lead screw;

means, including a guide slot in the switch housing, and a pin having one end anchored in the indexing nut and the other end extending into the guide slot, for preventing rotation of the indexing nut as it is displaced longitudinally in accordance with rotation of the lead screw;

a cam body, including a plurality of interior tangs exa plurality of electro-mechanical switches having tending into the respective longitudinal SlOtS Of the their respective actuator portions disposed adlead screw, and having at least one exterior lobe; means, including a bearing having its inner portion received in the indexing nut and its outer portion 5 received in the cam body, for translating longitu- Slgnals. as the lead Screw. ls rotated m acdinal displacement of the indexing nut into loncordance wlth motor Shaft rotation gitudinal displacement of the cam body; and

jacent the cam lobe path of travel, for selective actuation of the individual switches to provide con- 

1. A switch assembly for providing control signals as a function of angular motion, comprising: a lead screw, having a first portion positioned to receive rotational drive, and a second portion which is both threaded and defines at least one longitudinal slot; an indexing nut, having a threaded bore portion dimensioned to receive the exterior threads of the lead screw; means for preventing rotation of the indexing nut as it is displaced longitudinally by rotation of the lead screw; a cam body, spaced from the indexing nut, including at least one interior tang portion extending into the longitudinal slot of the lead screw, and having at least one exterior lobe; means, engaging both the cam body and the indexing nut, for effecting longituDinal displacement of the cam body as a function of the longitudinal displacement of the indexing nut, concomitantly with the angular displacement of the cam body as the lead screw is rotated; and a plurality of switches disposed adjacent the path of travel of the lobe on the cam body, for selective actuation by the lobe to provide the control signals as the lead screw is rotated.
 2. A switch assembly as claimed in claim 1, in which said lead screw defines a plurality of additional longitudinal slots, and said cam body includes a plurality of additional interior tang portions extending into the respective additional longitudinal slots of the lead screw.
 3. A switch assembly as claimed in claim 1, in which the means for preventing rotation of the indexing nut includes a guide slot in the switch assembly, and an indexing pin, having one end received in the indexing nut and the other end extending into the guide slot, thus to prevent rotation of the indexing nut as it is driven by rotation of the lead screw.
 4. A switch assembly as claimed in claim 1, in which the means for effecting longitudinal displacement of the cam body includes a bearing, positioned between the cam body and the indexing nut, and a pair of snap rings, to assist in translating the longitudinal motion of the indexing nut to the cam body.
 5. A switch assembly for providing control signals to de-energize a motor responsive to a preassigned rotational displacement of the motor shaft, comprising: a housing for the switch assembly; a lead screw, having a first portion positioned to receive rotational drive as a function of motor shaft rotation, and a second portion which is both threaded and defines a plurality of longitudinal slots; an indexing nut, having a threaded bore portion dimensioned to receive the exterior threads of the lead screw; means, including a guide slot in the switch housing, and a pin having one end anchored in the indexing nut and the other end extending into the guide slot, for preventing rotation of the indexing nut as it is displaced longitudinally in accordance with rotation of the lead screw; a cam body, including a plurality of interior tangs extending into the respective longitudinal slots of the lead screw, and having at least one exterior lobe; means, including a bearing having its inner portion received in the indexing nut and its outer portion received in the cam body, for translating longitudinal displacement of the indexing nut into longitudinal displacement of the cam body; and a plurality of electro-mechanical switches having their respective actuator portions disposed adjacent the cam lobe path of travel, for selective actuation of the individual switches to provide control signals as the lead screw is rotated in accordance with motor shaft rotation. 